Nextra Teleservices — not getting refund after disconnection

Address:

South West Delhi, Delhi, 110043

At the time of new connection nextra company charged me rs 1500 as security fees against the modem. On 26 feb i disconnected my nextra broadband and submitted the modem in the company.. They gave me a slip and told me to wait for 90 days for refund to receive in my account.. But now it's 180 days since i was assured for refund. I called nextra
Customer service several times every time they told me to wait 2 to 3 days and now they are not even picking up my call.
Details of my connection is as following
Name - subhash
Nextra customer no[protected]
Registered mobile no - [protected]
I look forward for your replies
Thanking you
Your's faithfully
Subhash